1. Field of the Invention
The present invention relates to an offline teaching method for, when a workpiece is automatically welded by a welding robot, making the welding robot memorize a weld line, which is the target of the work, and to an offline teaching method by which teaching using the welding robot can be performed in a safe and precise manner.
2. Description of the Related Art
As illustrated in FIG. 23, a workpiece 1 to be welded is set in a positioner 2, which adjusts the attitude thereof. A welding robot 3 having a welding torch is arranged close to the workpiece 1 set in the positioner 2. The welding robot 3 is set on a slider 4 whose movement allows the welding robot 3 to move in parallel to the workpiece 1 at positions close to the workpiece 1. If the reach of the welding robot 3 is insufficient (if the welding torch does not reach a weld line to be welded), the welding robot 3 itself moves relative to the workpiece 1 to allow the welding torch to complete a movement along a weld line.
The slider 4 may be one having three-degree-of-freedom X, Y, and Z axes that are perpendicular to one another and enable transfer as illustrated in FIG. 23, or may be one having a rotation axis for rotating the robot as well as the transfer axes as illustrated in FIG. 24. The slider 4 serves as an auxiliary axis that moves the welding robot 3.
On the other hand, the positioner 2 holds the workpiece 1 and allows the attitude of a weld line during welding to have an angle that suits the welding. As illustrated in FIG. 25, most popular positioners are doubly supporting one-axis positioners that each have a single rotation axis and that support a workpiece from both sides.
In addition, as illustrated in FIG. 26, there is also a two-axis positioner 2a that has two rotation axes and that allows the attitude of a weld line to have an arbitrary angle. Furthermore, positioners have been improved recently and, as illustrated in FIG. 27, there is a five-axis positioner 2b that has five rotation axes. In this case, a vertical first axis 2c is located at the center, and a first positioner 2d that includes a second axis and a third axis and a second positioner 2e that includes a fourth axis and a fifth axis are arranged on both ends of the first axis 2a, respectively. The first positioner 2d and the second positioner 2e can rotate around the first axis 2c. When a workpiece is being set in either positioner, a welding robot automatically welds a workpiece set in the other positioner. When both operations have been completed, the rotation angle (first axis) at the base rotates such that the newly set workpiece is positioned on the welding robot side and the welded workpiece is moved to a delivery position (workpiece setting position) side. At this time, the positioner that is holding the welded workpiece drives the two axes thereof to set the workpiece in a delivery device. In this five-axis positioner, for example, the first positioner 2d including the second axis and the third axis can serve for automatic welding by the robot and, at the same time, the second positioner 2e including the fourth axis and the fifth axis can serve for correction welding that is manually performed. In addition, although not illustrated, there are positioners that each have a transfer axis for moving a workpiece. Thus, a positioner can be defined as a device for moving a workpiece.
The workpiece 1 to be welded is, for example, a component of a construction machine, and a component of a construction machine generally has a complicated shape as illustrated in FIG. 28. Connections between an upper board and a side board or connections between a lower board and the side board are weld lines. Since the upper board, the lower board, and the side board in a component of a construction machine have curvatures, the weld lines are curves both in a plan view and in a side view. This workpiece is fixed in a clamping jig and mounted in a positioner, and then automatically welded by the welding robot.
If the welding robot performs automatic welding, a groove between materials 5 and 6 to be welded is oriented upward and a positioner is rotated such that the attitude of a torch 7 of the welding robot is oriented downward as illustrated in FIG. 29. Flat welding is then performed on the workpiece (materials 5 and 6 to be welded).
In addition, if horizontal fillet welding is performed on a weld line, the positioner is rotated in a manner similar to above so that the attitude of a workpiece illustrated in FIG. 30 is achieved for welding, and then horizontal fillet welding is performed. In the case of horizontal fillet welding, because, if the welding is performed at high current and high speed, beads may trickle down and therefore it is difficult to adjust the shapes of the beads, the positioner is rotated and flat welding is performed, if possible.
If a workpiece to be welded is bent boards as illustrated in FIG. 28, in order to successively perform flat welding using the welding robot, it is necessary to maintain the same inclination of weld lines in grooves and to make the robot and the positioner move in a coordinated manner before and after bent portions. In addition, if weld lines are long enough to exceed the reach of the robot, the slider needs to operate in a coordinated manner, too.
In order to perform these operations of the robot, teaching is needed. Teaching for the robot using an actual machine is performed by using a teaching pendant attached to a controller of the robot, guiding the robot, and making the robot memorize welding lines, which are work lines. In order to make the robot memorize work lines, the robot is guided to points through which the robot is to pass one by one, while an operator presses a position memorizing button at each point. A memory in the controller stores each position and a program is created.
However, as described above, since a component of a construction machine is likely to be large and a slider, a positioner, and the like are likely to be attached, which means that there are a lot of axes to be operated, skill in the operation is required. In addition, in the case of a large-sized workpiece, a positioner to be used is also large, and it is not rare that the workpiece is located at a position higher than the operator's head. The operator needs to go up to a high portion of the workpiece and then go down again, which is not easy work. In addition, there is a risk that the operator may fall from a high position.
Therefore, instead of teaching work using an actual machine, offline teaching, in which teaching is performed using a personal computer, is attracting attention as an effective method. As illustrated in FIG. 31, offline teaching is performed using a 3D model robot system and a workpiece displayed on a screen of a personal computer 11. A program created through offline teaching is transferred to a robot 13 through a communication cable connected to the personal computer 11 and a controller 12. After that, the robot 13 is used to move the torch on an actual workpiece without discharging arc in accordance with the program in order to check if the created teaching is correct.
Offline teaching is a significantly effective function because the robot and the positioner can be moved in a short period of time. For example, the rotational speed of a positioner for an actual large-sized workpiece is 3 rpm and therefore it takes 20 seconds to make the positioner rotate one revolution, whereas, in the case of offline teaching, the positioner can rotate one revolution in an instant. In addition, in the case of guiding the robot to a weld line, it is necessary, in teaching using an actual machine, to slow down the robot around a workpiece in order to avoid collision, and to accurately position the robot, which takes much time. In the case of offline teaching, however, the robot can move to a certain position just by clicking a surface of a workpiece model on the personal computer and therefore it takes little time, which is advantageous.
However, in the case of offline teaching, there has been a problem in that it is difficult to obtain an attitude that suits welding and appropriate angles of the torch and to perform checking.
In the case of offline teaching, although it is possible to see a workpiece from an arbitrary viewpoint, there is a problem in that it is hard to instinctively recognize, on a two-dimensional display, the angle of a weld line relative to the ground. That is, although it is easy to understand that the welding attitude is downward in the case of a simple workpiece as in FIG. 29, if a weld line is on bent boards as in FIG. 28, it is virtually impossible to make the welding attitude be oriented downward through visual recognition using a screen, and therefore a quantitative index of the attitude is needed.
The reason why a quantitative attitude is needed when flat welding is performed on the workpiece illustrated in FIG. 29 is not because the inclination of the weld line is simply made parallel to the ground, but because the weld line needs to be intentionally inclined downward in the forward direction by 1° to 3° in order to control the shape of beads.
Therefore, the inventors have already proposed an invention disclosed in Japanese Unexamined Patent Application Publication No. 2006-72673. That is, a method for setting a positioner for a welding robot disclosed in Japanese Unexamined Patent Application Publication No. 2006-72673 is a method for setting a positioner for a welding robot in which a workpiece to be welded is set in the positioner for the welding robot and the position of the positioner is determined such that the workpiece is arranged in a desired manner in relation to a welding torch. The method includes the steps of reading, by a computer, a three-dimensional model of the workpiece as well as information regarding a mechanism of the positioner, specifying either a weld surface or a weld line of at least one of materials to be welded in three-dimensional model, determining, by calculation, a reference line for determining an inclination of a portion to be welded on the basis of information regarding the specified weld surface or weld line, setting, if angles between the reference line and a vertical direction in terms of two directions that are perpendicular to each other are assumed to be α and β, target angles of α and β, and obtaining, by calculation, a single position or a plurality of positions of the positioner at which α and β are within certain ranges of the target angles by moving the workpiece model within a range limited by the mechanism of the positioner.